AbstractSet抽象类

package java.util;
//抽象类，实现了Set集合，继承于AbstractCollection抽象类
public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {

    protected AbstractSet() {
    }

    // Comparison and hashing
    public boolean equals(Object o) {
        if (o == this)
            return true;

        if (!(o instanceof Set))
            return false;
        Collection<?> c = (Collection<?>) o;
        if (c.size() != size())
            return false;
        try {
            return containsAll(c); //如果是集合对象，size相等，集合c是this的子集即两个集合元素完全相同
        } catch (ClassCastException unused)   {
            return false;
        } catch (NullPointerException unused) {
            return false;
        }
    }
    //计算hashCode，所有非null元素的hashcode之和
    public int hashCode() {
        int h = 0;
        Iterator<E> i = iterator();
        while (i.hasNext()) {
            E obj = i.next();
            if (obj != null)
                h += obj.hashCode();
        }
        return h;
    }
    public boolean removeAll(Collection<?> c) {
        Objects.requireNonNull(c);
        boolean modified = false;

        if (size() > c.size()) {
            for (Iterator<?> i = c.iterator(); i.hasNext(); )
                modified |= remove(i.next());
        } else {
            for (Iterator<?> i = iterator(); i.hasNext(); ) {
                if (c.contains(i.next())) {
                    i.remove();
                    modified = true;
                }
            }
        }
        return modified;
    }

}